1. Field of the Invention
This invention relates to the field of intravenous catheters, and more particularly, to balloon angioplasty catheters with autoperfusion and flow measurement capabilities.
2. Description of the Related Art
The use of balloon dilatation angioplasty as an alternative to heart bypass surgery has increased as improved catheter systems and techniques have been developed to advance the probability of success of such non-surgical solutions to blockage in arteries supplying blood for the heart. Balloon angioplasty involves the insertion of a catheter into the area of stenosis in the artery and inflation of a balloon incorporated near the distal tip of the catheter. This procedure provides a means of dilating the plaque on the artery wall, thereby providing a greater area through which blood may flow in the artery. The balloon is usually inflated through a lumen within the catheter by pumping fluid into the lumen from an external source located outside of the body. A common fluid used for this inflation is radiopaque dye.
A variety of techniques and apparatus suitable for balloon angioplasty have been developed and one problem with the basic balloon dilation catheters has been caused by blood stoppage through the artery when the balloon is being inflated. Thus, it is generally necessary to limit the amount of time that the balloon can be inflated in order to limit the possibility of angina or further heart damage. In order to increase the amount of time available for balloon inflation without causing these undesirable side effects, autoperfusion catheter systems have been developed which incorporate a conduit for blood flow past the balloon subsystem in the distal end of the catheter. Such autoperfusion catheters incorporate an entry upstream of the balloon, a lumen within the portion of the catheter incorporating the balloon, an exit to the lumen located near the distal end and downstream of the balloon.
Thus, a passage for the flow of blood is provided to bypass the inflated balloon, thereby providing an opportunity to keep blood flowing to the heart muscle while the balloon is being inflated during the angioplasty procedure.
While such autoperfusion catheters are an improvement over previous non-perfusion catheters, they nonetheless do not guarantee an adequate flow of blood past the balloon since, for example, the small orifices and lumen associated with the bypass of blood may become occluded without an immediate external indication. Flow may also be compromised if the entry or exit holes in the lumen are positioned too close to the artery wall or plaque. Such problems would not easily be detected externally from the body except for the subsequent complaints of chest pain by the patient. Such complaints may be delayed in patients with high pain threshholds and/or by the concomitant use of drugs. Therefore, there is a need for a means of directly and continuously measuring the blood flow in an autoperfusion catheter for use as a monitoring tool to help optimize the autoperfusion feature of the catheter during a balloon dilatation angioplasty procedure. To be effective, such a flow measurement means should be simple, small, easily incorporated in an otherwise standard autoperfusion balloon dilatation angioplasty catheter system and should be amenable to a variety of outputs that could be monitored by the physician performing the angioplasty or an assistant. The measurement should be quantitative or qualitative, the latter providing trend information.